The present invention relates to a transceiver module for optical communication. Particularly, the present invention relates to a transceiver module in which the coupling of a rod lens and a ferrule is improved, and the coupling efficiency of signal light is improved. Also, the present invention relates to a transceiver module for optical communication adapted to subscriber communications using optical fibers, sensing heads, and so on.
Recently, optical communication using optical fibers has come into wide use rapidly, and has begun to be brought into personal use such as telephone and facsimile, and into mass media such as television information. In addition, also in enterprises, there has come into use such an optical LAN (Local Area Network) system that terminal equipments are disposed in respective factories, respective sections and so on, and the equipments are connected through optical fibers, so that information can be exchanged in real time. In such a case, it has been a problem for wider use to realize a transceiver module constituted by a fiber coupler and so on for coupling an optical fiber with a light-emitting element and a light-receiving element of a terminal equipment installed in each home or the like, the module having a high efficiency of coupling and being reduced in cost.
A system called a pig tail type as shown in FIG. 17, or a system for bringing a lens and a ferrule of zirconia into physical contact as shown in FIG. 18, has been considered as an optically coupling circuit.
In a transceiver module of the pig tail type as shown in FIG. 17, a light-emitting element 1021, a light-receiving element 1022 and a coupling optical fiber 1023 are attached to a casing 1025 so that the the light-emitting element 1021 and the light-receiving element 1022 are coupled with the top end of the coupling optical fiber 1023 through a half mirror 1024 respectively. This coupling optical fiber 1023 attached to the casing 1025 forms a loop 1026 in order to prevent the coupling optical fiber 1023 from being broken off by bending. The coupling optical fiber 1023 is coupled with an external optical fiber line for transmission through an adaptor 1027.
On the other hand, in a transceiver module of the system for bringing a lens and a ferrule into physical contact as shown in FIG. 18, a light-emitting element 1021 and a light-receiving element 1022 are attached to a casing 1025 so that the light-emitting element 1021 and the light-receiving element 1022 are optically coupled with a lens 1028 through a half mirror 1024. A ferrule 1029 consisting of zirconia is also brought into physical contact with the top end of the lens 1028. Accordingly, if the top end of an optical fiber 1030 is inserted into the ferrule 1029 from the outside, the optical fiber 1030 can be coupled. The abutment surfaces of the lens 1028 and the zirconia ferrule 1029 are ground into convex spherical surfaces respectively in order to obtain physical contact.
In the above-mentioned pig tail type, the coupling optical fiber 1023 between the adaptor 1027 and the casing 1025 is apt to be broken when the coupling optical fiber 1023 is bent into an S-shape. It is therefore necessary to make the coupling optical fiber 1023 into the loop 1026 to couple the casing 1025 and the adaptor 1027. Accordingly, there is a problem that a space for the loop is required so that the module is made large.
Further, there is a problem that the number of parts such as the coupling optical fiber, the adaptor and so on becomes so large as to increase the cost.
On the other hand, in a module in which a lens and a zirconia ferrule are brought into physical contact, the module can be made small in size and in the number of parts. However, a marketed ferrule has a ground surface with a curvature radius R the center of which is deviated. If the center deviation of the ground surface is about 50 .mu.m, there appears a gap between the lens and the core of an optical fiber, so that signal light is reflected on the end surface of the optical fiber. Accordingly, there is a problem that the efficiency of coupling is deteriorated, and this reflected light acts as return light so as to give a noise to a semiconductor laser.
In addition, a change of surrounding temperature makes the lens and the ferrule expand and contract, so as to change this gap. Therefore, there is also a problem that the temperature characteristic of the transceiver module is also deteriorated.
FIG. 19 shows the basic structure of a transceiver module for optical communication, which is constituted by a light-emitting element 1 such as a semiconductor laser for emitting transmission signal light, a light-receiving element 2 such as a photodiode, a phototransistor, or a photocell for receiving detection signal light through a half mirror 8, a coupling lens 3 for connecting the transmission signal light to a light transmission path (not shown) such as an optical fiber, and a monitor light-receiving element 6 for monitoring the quantity of light emission of the light-emitting element 1.
In order to reduce the distance L between the light-emitting element 1 portion and the coupling lens 3 along the axis of a beam emitted from the light-emitting element 1 provided for emitting transmission signal light, there has been proposed a semiconductor laser device for perpendicularly reflecting light emitted from the light-emitting element 1, as described, for example, in Japanese Patent Unexamined Publication No. Hei 5-129711. The structure thereof is shown in FIG. 20.
In FIG. 20, reference numeral 71 designates a heat radiation plate which is formed by plating a surface of a heat-conductive metal plate such as a carbon steel plate, a copper plate, or an aluminum plate with a metal such as gold. A sub-mount 73 is fixed onto an upper surface of the heat radiation plate 71. A semiconductor laser chip 74 is fixed sideways onto an upper surface of the sub-mount 73 so that a laser light beam from the front cleavage surface of the semiconductor laser chip 74 is emitted in a direction substantially parallel to the upper surface of the heat radiation plate.
The rear cleavage surface of the semiconductor laser chip 74 is perfectly blocked by a reflection film so that all laser light beams are emitted from the front cleavage surface. On the other hand, a monitor photodiode 77 is mounted to a reflection portion mounting portion 76 within a frame body of a cap substance 72 so that a great part of the laser light beam emitted from the front cleavage surface of the semiconductor laser chip 74 is reflected on a surface of the photodiode 77 so as to go toward a glass plate 78 attached on the cap body 72 and the residual part of the laser light beam is received by the photodiode 77. Thus, the photodiode 77 serves as a laser light reflecting portion and also as a monitor light-receiving element. A current for driving the semiconductor laser device is controlled by the output of the photodiode 77 to attain the stabilization of the laser light beam outputted from the semiconductor laser device.
Also in the case of a transceiver module for optical communication formed by using the semiconductor laser device having the aforementioned structure, as shown in FIG. 19, detection signal light transmitted from the light transmission path is reflected by a half mirror disposed between the light transmission path such as an optical fiber and the reflecting portion (that is, generally, between the coupling lens and the light transmission path) so that the reflected light can be received by a light-receiving element provided separately.
As described above, in the conventional transceiver module for optical communication, the light-receiving element portion is separated by a half mirror or the like in the front of the light transmission path so that a light path different from the path of light emitted from the light-emitting element portion is formed. Accordingly, there arises a problem that the number of constituent parts is increased to thereby bring an increase in the number of assembling steps and an increase in apparatus size.